Process for treating nickel-iron-molybdenum alloy to increase induction rise and pulse permeability



Dec. 8, -1970 F. PFI-:IFER ETAL 3,546,031

, PROCESS FOR TREATING NICKEL-IRONMOLYBDENUN ALLOY T0 INCREASE INDUCTION RISE AND PULSE PERMEABILITY Filed oct. 1s, 19e? v o o Cl yQ Y o 8 so O o o I0 m O m v o 3 o 1 l O L O m o 1 (D LLI 2 n g o 9 2 Lao 9 m m i l (D (D g g 33 A 2 V I\/ 9 8 i- E 1 q E E g g 8 2 C5 D O S o o o o' o n s s 5 f am ELS gm D' n' (m) Ei E5 i i 52 E9 59 l I I I L l x I l Q o o o o o o 8 8 3 8 8 lf) l0 N fruluavawaad 24S-md wlTNEssEs INVENToRs Friedrich Peifer ond Rudolf Deller Wf/W ATTORNEY United States Patent O M Int. Cl. C21d 1/04; C22f 1/10; H01f 1/00 U.S. Cl. 148-108 5 Claims ABSTRACT OF THE DISCLOSURE Nickel-iron-molybdenum alloy strip which has been previously subjected to an annealing treatment at a temperature between 950 C. and 1,220 C., is reheated to a temperature above the Curie point and then rapidly cooled to 200 C. or below. The alloy strip is then subjected to a final anneal at a temperature of about 400 C. to 500 C. This final anneal may be carried out on the alloy strip in a magnetic field wherein the lines of force are transverse to the direction in which the magnetic linx will travel in the strip when it is in use in a magnetic core.

BACKGROUND OF THE INVENTION Alloys having a large induction rise and a large pulse permeability are required in electrical applications, as for use in choke coils, employing bias with DC fields, as well as in pulse transformers which operate in a unipolar fashion. For example, the larger the induction rise from the remanence for a transformer material and the greater the pulse permeability, the smaller the number of windings required for a given iron cross-section in order to transmit a specified voltage-time area.

The high permeability nickel-iron alloys and ferrites which are employed in the manufacture of unipolar pulse transformers have not been entirely satisfactory with regard tothe requirement for a short rise time and a small pulse slope coupled with large modulability, and thus are not suitable for transformers with a large bandwidth. In this regard, according to H. Stegmeier (Archiv der Elektrischen bertragung 1965 page 257) a tapewonnd core made from a nickel-iron-copper-molybdenum alloy strip of thickness 0.03 mm. possesses, Without bias, an induction rise of only 2,000 gauss, and a tape-wound core of the same alloy but having a strip thickness of 0.003 mm. exhibits an induction rise of only 400 gauss.

Also, accoridng to H. Stegmeier, the most favorable induction rise value exhibited ferrites is merely 3,000 gauss. However, these induction rise values characterizing the prior art materials are inadequate for high quality pulse transformers to be employed in the new low-leakage uncut magnetic circuits.

a soft magnetic nickel-iron alloy having a large induction rise, and a large pulse permeability or, the equivalent, a high incremental permeability up to the highest possible modulating fields or induction values.

In accordance with this invention, the desired characteristics are obtained subjecting a known soft magnetic nickel-iron-molybdenum alloy to a high temperature heat treatment between about 200 C. and the Curie point (below about 600 C.) of the said alloy, after which the alloy is subjected to an additional heat treatment or a combined heat treatment and magnetic treatment (magnetic anneal).

3,546,031 Patented Dec. 8, 1970 Following the teachings of this invention, the induction rise of a nickel-iron-molybdenum alloy consisting of 61 to 67% nickel, 2 to 4% molybdenum, balance iron and containing the usual deoxidizing and processing additions, and small amounts of incidental impurities is increased from the usual value of 2,000 to 3,000 gauss to more than 5,000 gauss and, in some cases, to more than 8,000 gauss. In carrying out the process of the invention, a magnet core made from the nickel-iron-molybdenum alloy defined above, is annealed for several hours in a preliminary treatment for from 4 to 6 hours at a temperature for from 4 to 6 hours at a temperature between 9.50 and 1,220 C., after which the said alloy is heated to a suitable temperature above the Curie point, for example to about 750 C., and then rapidly cooled from this temperature to 200 C. or below, the said cooling being effected, for example, in about 5 minutes. Thereafter the said alloy is subjected to a final anneal of several hours duration, about 3 to 5 hours, for example, in the temperature range 400 to 500 C., and preferably from 450 C. to 500 C. This final heat treatment is particularly beneficial when carried out in a magnetic field the lines of force of which, in the hot alloy, run transverse to the subsequent direction of the magnetic flux.

The heat treatment which such a nickel-ron-molybdennm alloy is subjected in accordance with the invention and prior to its use may also be put into effect following somewhat different procedures. Thus, the alloy strip material or the magnet core made from it, which has already been subjected to a high temperature anneal at a temperature of from 950 to 1,220 C. in au atmosphere, having a low partial pressure of oxygen, can first be cooled to about 200 C. or to a temperature below 200 C. and thereafter heated to a prescribed temperature above the Curie point, for example, to 750 C. The said alloy is then cooled in a few minutes to about 200 C. and finally annealed for a number of hours at a temperature below the Curie point, preferably in the range 450 to 500 C., this latter annealing being preferably carried out in a magnetic field whose lines of force in the hot sample run transversely to the subsequent direction of the magnetic flux. It has also been found feasible to cool at a desired rate subsequent to the high temperature anneal and then to subject the alloy, or the magnet core made from it, to a transverse magnetic field for several hours at a temperature below the Curie temperature.

Surprisingly it has been found that heat treatment in a transverse magnetic field is beneficial both in obtaining a high induction use and in obtaining a relatively high pulse permeability.

The primary object of the invention is a process for manufacturing a soft magnetic alloy material which, over the entire thickness range from 0.1 to 0.003 mm., displays an induction rise from the remanence (Br) which is greater than 3,000 gauss and, more especially, one of ,5,000 to 12,000 gauss and which, in addition, possesses a high pulse permeability.

BRIEF DESCRIPTION OF THE DRAWING The figure presents a series of curves in which Apulse permeability ,MJ is plotted against induction rise, AB,

for a series of nickel-iron-molybdenum alloy strips of three different strip thicknesses, each at two values of pulse duration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ability set forth in Table II by an was determined by field. It can be seen from the shapes of the curves that, means of a Maxwell bridge at 0.5 moe and 70 Hz.; it is over the whole range of measurement, as a result of the essentially the same as the initial permeability. In addiheat treatments and magnetic annealing carried out in tion, as to practical working characteristics, the pulse accordance with the invention, almost the same value is permeability obtained for the maximum induction variation, and, fur- AB ther, that the thinner' s trips are characterized by having a MJ: ,no XH higher pulse permeability.

The benefits to be obtained via the procedures carried Was measured for a Dumber f Samples, With Varied indue' out in accordance with the invention do not reside only tion, AB, While keeping the PUiSe duration fd Constant in the great improvement in the induction rise at a favorand in the region 0f 1 i0 50P- SeC- (In the equation fol' able pulse permeability, but also in the fact that, by a the Pulse Permeability lU-J, #o delffes the Permeability 0f suitable choice of heat treatment or heat treatment cornemPY Space and AH the Change 1H iieid Strength-J bined with a magnetic anneal, it is possible to attain a EXAMPLES desired .induction rise combined .with a suitable pillse permeability, or to produce a desired pulse permeability Polif Nl'Fe'MO mgots A B, C and D Whose Compos" in association with a satisfactory induction rise. As may mlsdu; W; Percet lr' wen m dTalle I bwllwre be seen from Table II, the heat treatment at a temperature To e o, mm' m 1C ness an en CO 'ro e W1 more remote from the Curie point leads to a larger inmtermedlate anneals to a ,final thickness of 0'05 003 duction rise than does a temperature nearer to the Curie 0.015 and 0.006 mm. respectively. Point TABLE I The nickel-iron-molybdenum alloy strip produced in accordance with the invention is suitable for chokes having Nickel Molybdenum Manganese Iron D.C. bias as well as being suitable for chokes and pulseg. it; 005g Bflnce. transformers which have unpolar operation. The advan- 64160 2:59 0:55 D0: 25 tage to be gained by the use of such alloy strip for uni- 64- 90 2 59 i149 D0- polar pulse transmission lies mainly in the fact that its very large induction rise, in combination with the satis- Tape-wound cores made from the alloys of Table I are factory pulse permeability, serves to transmit apprecably annealed for 5 hours at 1,000 to 1,200 C. in hydrogen, larger voltage-time areas (integrated voltage-time pulses) furnace cooled to about 200 C., and finally reheated to 30 than hitherto, and in a still shorter time. 750 C., after which they are cooled in about 5 minutes We claim as our invention: from 750 C. to about 200 C. by inserting them into a 1. A process for producing a nickel-iron-molybdenum water-cooled container. After making room-temperature alloy strip characterized by a large induction rise having measurements of the magnetic characteristics (which apvalues ranging from 5,000 to 12,500 gauss and a large pear in columns 6 and 7 of Table II below), a subsequent 35 pulse permeability value, the alloy containing, by weight, series of treatments is given in the temperature range 400 61% to 67% nickel, 2% to 4% molybdenum and the balto 500 C., both in the absence of an external magnetic ance iron with small amounts of incidental impurities, the field and in the presence of a magnetic field provided by steps comprising, subjecting the alloy strip to a high teman alnico permanent magnet, the said magnetic field being perature anneal at a temperature of from 950 C. to transverse to the subsequent magnetization direction of 1,220 C. for a period of from 4 to 6 hours, reheatng the samples. The values of induction rise and of the permethe alloy to a lower temperature range but above the Curie abilities evaluated at the conclusion of this tempering temperature and quenching therefrom to a temperature treatment are presented in the last two columns of Table below about 200 C. and thereafter annealing the alloy 1I. The data obtained in these tests is summarized in Table strip for a period of hours in a temperature range lying II hereafter. between the Curie point of the alloy and 200 C.

TABLE 1i Heat treatment and combined heat and magnetic treatment (maglnetirann'ealipg) oi tape-wound cores made from the Nl-Fc-Mo alloy strip material iste in a e Magnetic properties after cooling from .Auneallng without Anncaling with Magnetic values after 750 C. transverse field transverse field tempering High temp. anneal Strip a AB Temp., C. Time, hrs. Temp., Time, p., A B Example Alloy thickness,rrim. Temp., C. Time,hrs. (Gauss) C. hrs. (Gauss) 0.05 1, 200 5 4, 300 2, 440 10,700 0.05 1,200 5 4,300 2,000 11,240 0.05 1,200 5 3, 780 4 4, 010 11,890 0.05 1,000 5 4, 085 4 4, 360 11,180 0.05 1,200 5 5,430 4 4,930 10,970 0. 05 i, 200 5 5, 805 4 2, 900 12,000 0.05 1, 200 5 5, 865 4 3, 280 12.300 0.05 1, 200 5 5, 865 4 3, 900 12,150 0.05 1,200 5 5, 805 4 4, 230 11,510 0. 03 ,100 5 5, 500 4 3, 770 11,000 0. 03 1,100 5 5,500 4 3, 940 11,000 0. 015 1,000 5 4,130 4 4,120 11,830 0. 015 i, 000 5 4,130 4 4, 050 9, S20 0.000 1,000 5 3, 360 4 4,610 10,305 0. 006 1, 000 5 3, 360 4 4,200 6, 735

Examples 12 to 15 of Table II and the curves of the 2. A process in accordance with claim 1 in which the figure illustrate the surprisingly large improvement in the final anneal is carried out in the temperature range from induction rise as a result of using the procedures in ac- 400 C. to 500 C. for a period of from 3 to 5 hours. cordance with the invention, the improvement being evi- 3. The process of claim 1 wherein the temperature dent for very thin samples as well as for the thicker strips. above the Curie point to which the alloy strip is heated Theycurves present the measured pulse permeability ,uJ is about 750 C. as a function of the induction rise AB for pulses of dura- 4. The process of claim 1 wherein the final anneal is tioii of 2 and 10 iisec, for tape-wound cores made from carried out in a magnetic field in which the lines of force strip of thickness 0.05, 0.015 and 0.006 mrn. respectively are transverse to the direction which magnetic flux will of alloy C, the said cores having been subjected to a highultimately flow in the alloy strip in use. temperature anneal of 5 hours duration followed by tem- 5. The process of claim 3 wherein the final anneal is pering fOr 4 hOurS at 48()g C. in a transverse magnetic 75 carried out in a magnetic field in which the lines of force are transverse to the direction which magnetic flux will ultimately flow in the alloy strip in use.

References Cited UNITED STATES PATENTS Elmen 75-170 Elmen 148-121X Parkin 148-108 Gibbs et al. 148-121X 10 [4S-11.5, 121

6 OTHER REFERENCES L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner U.S. C1. X.R. 

